Organic electroluminescent display device and chemical compounds for liquid crystals

ABSTRACT

The new organic electroluminescent display device has a carrier-transporting layer and/or an organic luminous layer composed of a nematic liquid crystal or a liquid crystal dispersing a carrier-transporting low-molecule therein. When the organic luminous layer is to be bestowed with faculty as a liquid crystal, it is made of a nematic liquid crystal. Both the carrier-transporting layer and the organic luminous layer may be bestowed with faculty as a liquid crystal. Since the liquid crystal is incorporated in the carrier-transporting layer and/or the organic luminous layer, the display device can be driven as a liquid crystal display device in a dark place by charging with a voltage lower than a light emission initiating potential. Of course, it is driven as an electroluminescent display device when it is charged with a voltage higher than the light emission initiating potential. Use of an electroluminescent liquid crystal as a organic luminous layer enables omission of a carrier-transporting layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 11/706,590filed Feb. 15, 2007, now abandoned, which is a continuation-in-part ofU.S. application Ser. No. 10/650,361 filed Aug. 28, 2003, now U.S. Pat.No. 7,195,826, which is a continuation of U.S. application Ser. No.09/844,151 filed Apr. 27, 2001, now abandoned, which claimed the benefitof Japanese Patent Application No. 2000-128766 filed Apr. 28, 2000.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an organic electroluminescent displaydevice which is also driven as a liquid crystal display device, and alsoto electroluminescent chemical compounds useful as liquid crystals.

DETAILED DESCRIPTION OF THE INVENTION

A conventional electroluminescent display device has the structure thata transparent electrode (an anode), a carrier-transporting layer, anorganic luminous layer and a backside electrode (a cathode) aresuccessively laid on a transparent substrate. A plurality of transparentelectrodes are aligned along X-X direction, while a plurality ofbackside electrodes are aligned along Y-Y direction, so as to make up XYmatrix.

When a driving current is supplied to a predetermined position on XYmatrix through the transparent and backside electrodes, a hole from theanode recombines with an electron from the cathode in the organicluminous layer. An organic luminous molecule, which is excited by therecombination, emits light. The light is emitted through the transparentelectrode and the transparent substrate to the outside.

Since the organic electroluminescent display device has the feature thatthe organic luminous layer itself emits light, a clear image isreproduced as compared to the liquid crystal display device. However,power consumption for driving the organic electroluminescent displaydevice is unfavorably greater than that for the liquid crystal displaydevice using reflection of outside light.

The liquid crystal display device reproduces a clear image with highcontrast under a light condition, but an image is hardly distinguishedat night or in a dark place. Shortage of luminance is supplemented bybacklight in order to solve difficulty to distinguish an image. Use ofbacklight means increase of power consumption.

Such difficulty to distinguish an image is overcome by lamination of anelectroluminescent element on a liquid crystal display device, asdisclosed in Utility Model Publication No. 59-181422. The proposedliquid crystal display device reproduces an image distinguishable indark place, due to planar emission of the electroluminescent element.The liquid crystal display device is also made thinner than a knownliquid crystal display device having an electroluminescent elementprovided at the back side, since the electroluminescent element isdirectly laid on the liquid crystal display device.

The liquid crystal display device disclosed in Utility Model PublicationNo. 59-181422 is fabricated by positioning a liquid crystal elementcomposed of a transparent electrode, an oriented film, a polarizingplate, a spacer and a liquid crystal layer between a couple of glasssubstrates, and then forming an electroluminescent element on one of theglass substrates. Since the electroluminescent element is merely laid onthe liquid crystal element, such the liquid crystal display device isnecessarily manufactured by a complicated process with increased numberof lamination. The increased number of lamination makes it difficult toreduce a thickness of the display device.

SUMMARY OF THE INVENTION

The present invention aims at provision of a new electroluminescentelement, which reproduces a distinct image with reduced powerconsumption, and also provision of electroluminescent chemical compoundsuseful as liquid crystals. An object of the present invention is tobestow a carrier-transporting layer and/or an organic luminous layerwith faculty as a liquid crystal, so that the new display device acts asan electroluminescent display device at night or in a dark place withoutlighting and also as a liquid crystal display device at a daytime or ina lighting place.

The newly proposed organic electroluminescent display device has one orboth of a carrier-transporting layer and an organic luminous layerbestowed with faculty of a liquid crystal, so as to be driven as aliquid crystal display device or as an electroluminescent display devicein response to magnitude of a drive voltage. The display device may bedriven by either a simple matrix method or an active matrix method.

For instance, it is driven as a liquid crystal display device, whichreproduces an image with variable contrast, at a voltage lower than alight emission initiating potential, and as an electroluminescentdisplay device at a voltage higher than a light emission initiatingpotential, due to the feature of a conventional organicelectroluminescent element which need a higher drive voltage. Suchchange of display mechanism saves power consumption.

Of course, it is predicted that the organic electroluminescent elementcan be driven at a voltage lower than that for a liquid crystal withprogress of technology on an organic electroluminescent element. In sucha case, display mechanism will be switched between theelectroluminescent display device and the liquid crystal display device,accounting distinctness of an image.

The new organic electroluminescent display device having acarrier-transporting layer bestowed with faculty as a liquid crystal isof the structure that at least one carrier-transporting layer composedof a liquid crystal and at least one organic luminous layer aresandwiched between a transparent electrode and a backside electrode eachheld in parallel to the other. The organic luminous layer is made of apolymer, a low molecule-dispersed polymer or a bilayer of a polymer anda monomer. The carrier-transporting layer disperses a nematic liquidcrystal or a low-molecular carrier-transporting substance therein.

The new organic electroluminescent element having an organic luminouslayer bestowed with faculty as a liquid crystal is of the structure thatat least one carrier-transporting layer and at least one organicluminous layer composed of a liquid crystal are sandwiched between atransparent electrode and a backside electrode each held in parallel tothe other. In this case, the carrier-transporting layer is made of apolymer, a low molecule-dispersed polymer or a bilayer of a polymer anda monomer. The organic luminous layer contains a nematic liquid crystaltherein.

The new organic electroluminescent element having both of acarrier-transporting layer and an organic luminous layer bestowed withfaculty as liquid crystals is of the structure that thecarrier-transporting layer and the organic luminous layer, both of whichcontain liquid crystals therein, are sandwiched between a transparentelectrode and a backside electrode.

Two or more of different organic compounds may be included in a liquidcrystal layer, by blending a liquid crystal with an organic luminoussubstance for instance.

In case of using an electroluminescent liquid crystal compound as anorganic luminous layer, an electroluminescent display device may befabricated without deposition of a carrier-transporting layer. Thewording “electroluminescent” of such a liquid crystal means ability ofcarrier-transportation (including carrier-injection) and light emissionas a faculty of an electroluminescent device in this specification.

The newly proposed organic electroluminescent substance, which alsoperform liquid crystal faculty, are chemical compounds I-V havinggeneral structures under-mentioned. 12-OKB, 8-OKB and 16-OKB belong tothe chemical compound I, 18-OXD belongs to the chemical compound II,8-OCu belongs to the chemical compound III, 8-PNP-O12 belongs to thechemical compound IV, and TPD-8 belongs to the chemical compound V.

Chemical Compound I:

wherein R¹ is a straight-chained alkyl group containing 1-20 carbonatoms, R² to R⁹ is individually hydrogen or an alkyl group containing1-3 carbon atoms, and Ar¹ is a substituted or non-substituted aryl groupcontaining 6-14 carbon atoms.Chemical Compound II:

wherein R¹⁰ and R¹¹ are individually straight-chained alkyl groupscontaining 1-20 carbon atoms, and Ar² and Ar³ are individuallysubstituted or non-substituted aryl groups containing 6-14 carbon atoms.Chemical Compound III:

wherein R¹² is a straight-chained alkyl group containing 1-20 carbonatoms, and R¹³ to R¹⁷ are individually hydrogen or alkyl groupscontaining 1-3 carbon atoms.Chemical Compound IV:R¹⁸—Ar⁴—Ar⁵—O—R¹⁹wherein R¹⁸ and R¹⁹ are individually straight-chained alkyl groupscontaining 1-20 carbon atoms, and Ar⁴ and Ar⁵ are individuallysubstituted or non-substituted aryl groups containing 6-14 carbon atoms.Chemical Compound V:

wherein R²⁰ is a straight-chained alkyl group containing 1-20 carbonatoms, and Ar⁶ to Ar¹⁰ are individually substituted or non-substitutedaryl groups containing 6-14 carbon atoms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bird eye's view illustrating an organic electroluminescentelement partially cut off.

FIG. 2 is a view for explaining driving mechanism of an organicelectroluminescent display device.

FIG. 3 is a view illustrating a cell having both surfaces to whichpolarizing plates are stacked.

FIG. 4 shows a lamellar structure of an organic electroluminescentdevice fabricated in Example 7.

FIG. 5 is a graph illustrating voltage-current characteristic of anorganic electroluminescent device fabricated in Example 8.

FIG. 6 a graph illustrating relationship of light emission with avoltage applied to an organic electroluminescent device fabricated inExample 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The newly proposed electroluminescent display device is of structure asshown in FIG. 1. A transparent electrode 2 (an anode) is laid on atransparent substrate 1 such as glass or synthetic resin film, by vapordeposition of ITO or the like. After a carrier-transporting layer 3, anorganic luminous layer 4 and a backside electrode 5 (a cathode) aresuccessively laid thereon, the whole body is hermetically sealed with aprotective layer such as a glass or metal sheet.

The transparent electrode 2 is formed in a striped shape extending alongX-X direction, while the backside electrode 5 is formed in a stripedshape extending along Y-Y direction crossing X-X direction with a rightangle. The trilayer structure that an electron-transporting layer and ahole-transporting layer are placed at both sides of the organic luminouslayer 4 may be also adopted.

A gap between the transparent electrode 2 and the backside electrode 5is charged with a voltage by a driving circuit 5. When application ofthe voltage is controlled by signals representing an image, the organicluminous layer 4 is excited at a predetermined position on X-Y matrix.Light is emitted by excitation of the luminous layer 4 to reproduce theimage. A positive direct current is ordinarily used for the charging,but a reverse voltage may be superimposed to inhibit degradation of theorganic luminous layer 4.

One or more of under-mentioned polymers and copolymers are solely orcombinatively used for substance of the organic luminous layer 4. Apolymer-type organic luminous layer may be formed by application of aliquid to form a coating layer. Hereinafter, the word “polymers” used inthe specification of the present invention involves copolymers.

A Group of Polyparaphenylene Vinylene

A Group of Polyparaphenylene

A Group of Polyvinylcarbazole

A Group of Polythiophene

A Group of Polysilane

A Group of Poly Alkylfluorene

Copolymers

P(VK-co-OXD) (a random copolymer of 9-vinylcarbazole with oxadiazolevinyl monomer), PTDOXD (an alternate arrangement polymer of tetraphenyldiamine with oxadiazole)

A low molecule-dispersed polymer, which comprises a polymer dispersing alow molecule as a dopant, is also useful for formation of the organicluminous layer. A dopant for the purpose may be organic substanceshaving constitutional formulas as follows.

Use of a low molecule-dispersed polymer enables adjustment of a luminouscolor in correspondence with a kind and concentration of a dopant. Forinstance, a luminous color such as blue, green or orange is realized bydoping PVX (polyvinylcarbazole) with fluorochrome such as TPB(1,1,4,4,-tetraphenyl-1,3-butadiene), cumarin, DCM-1 or rubrene. In thecase where such a low molecule-dispersed polymer is used for an organicluminous layer, a luminous color from a part can be advantageouslydifferentiated from the other part by pre-doping the polymer withmultiple pigments so as to diminish fluorescent of a specifiedpigment(s) by irradiation with light of specified wavelength. A luminousplane may be properly patterned by partial irradiation using aphotomask.

The organic luminous layer may be of bilayer structure. For instance,when 1,2,4-triazoles/aluminum complex is deposited as a hole blockinglayer on a luminous layer composed of poly(N-vinylcarbazole) capable ofhole transportation, the luminous layer emits blue light. A luminouscolor is freely changed by selection of fluorochrome for dopingpoly(N-vinylcarbazole).

Faculty as a liquid crystal display device is realized by laying aliquid crystal layer containing a nematic liquid crystal on acarrier-transporting layer or an organic luminous layer which has beenused so far as organic electroluminescent substances, or by mixing suchthe liquid crystal in the carrier-transporting layer or the organicluminous layer. A carrier-transporting layer or an organic luminouslayer may be also made of a substance which acts as both a liquidcrystal and an electroluminescence. Such the substance may be a nematicliquid crystal prepared by the following process, for instance.

[Synthesis of a Carrier-Transporting Liquid Crystal 8-OKB(2-1,4-carbazole-4′-n-octyloxybiphenyl)]

After 4-bromo-4′-hydroxybiphenyl is dissolved in cyclohexanone,potassium carbonate and 1-iodine octane are added to the liquid andsubjected to reflux reaction in a nitrogen atmosphere. When the reactionis completed, a reaction product is dissolved in diethyl ether and thenfiltered. A recovered filtrate is separated from the solvent, refinedwith ethanol, and then recrystallized. A white solid (8-OB) is producedaccording to the formula of:

8-OB is blended with carbazole, palladium acetate, phosphine, sodiumtertiary butyrate and o-xylene, and subjected to reflux reaction in anitrogen atmosphere. At the end of the reaction, a reaction product isextracted in chloroform, washed with distilled water, refined by acolumn chromatography using chloroform and n-hexane at a ratio of 1:2,and then recrystallized to produce a white solid (8-OKB) according tothe formula of:

[Synthesis of a Carrier-Transporting Liquid Crystal 12-OKB(2-2,4-carbazole-4′-n-dodecaxybiphenyl)]

After 4-bromo-4′-hydroxybiphenyl is dissolved in cyclohexanone,potassium carbonate and 1-iodine decane are added to the liquid andsubjected to reflux reaction in a nitrogen atmosphere. At the end of thereaction, a reaction product is dissolved in diethyl ether and filtered.A recovered filtrate is separated from a solvent, refined with ethanoland then recrystallized to produce a white solid (12-OB) according tothe formula of:

12-OB is blended with carbazole, palladium acetate, phosphine, sodiumtertiary butyrate and o-xylene, and subjected to reflux reaction in anitrogen atmosphere. At the end of the reaction, a reaction product isextracted in chloroform, washed with distilled water, refined by acolumn chromatography using chloroform and N-hexane at a ratio of 1:2,and recrystallized to produce a white solid (12-OKB) according to theformula of:

[Synthesis of 18-OXD (2-1,2-(4-n-methyl octadecylaminophenyl)-5-(4-cyanophenyl)-1,3,4-oxadiazole)]

After N-methyl octadecylamine (Na) is dissolved in cyclohexanone,potassium carbonate and 4-bromo benzonitrile are added to the liquid andsubjected to reflux reaction in a nitrogen atmosphere. At the end of thereaction, a reaction product is dissolved in chloroform and filtered. Arecovered filtrate is separated from the solvent, and un-reacted mattersare sublimated. In this case, a yellow solid (Nab) is obtained accordingto the formula of:

The yellow solid (Nab) is blended with an excessive amount of sodiumazide and ammonium chloride, subjected to reflux reaction with heat indimethylformamide, and washed with distilled water and chloroform, toproduce a brown viscous matter (4 NabN) according to the formula of:

The product (4 NabN) is dissolved in pyridine, subjected to refluxreaction with heat in a nitrogen atmosphere. The reaction is continuedunder the condition that 4-cyanobenzoyl chloride dissolved in pyridineis being dropped. After completion of the reaction, a reaction productis separated from pyridine, and washed with distilled water andchloroform, to produce a brown viscous matter. The brown viscous matteris refined to a brown solid by a column chromatography using ethylacetate and n-hexane at a ratio of 3:2 and then recrystallized to ayellowish white solid (18-OXD) with methanol. The reaction to 18-OXD is:

[Synthesis of 8-OCu (2-2,4-cumarin-4′-n-octyl)]

After 4-cumarin is dissolved in cyclohexanone, potassium carbonate and1-iodine octane are added to the liquid, and subjected to refluxreaction in a nitrogen atmosphere. At the end of the reaction, areaction product is dissolved in tetrahydrofuran and filtered. Arecovered filtrate is separated from the solvent, and recrystallizedwith n-hexane, to produce a white solid (8-OCu) according to the formulaof:

[Synthesis of 16-OKB (2,3,4-carbazole-4′-n-dodecahexyl biphenyl)]

After 4-bromo-4′-hydroxybiphenyl is dissolved in cyclohexanone,potassium carbonate and 1-bromo dodecaxyl are added to the liquid, andsubjected to reflux reaction in a nitrogen atmosphere. At the end of thereaction, a reaction product is dissolved in diethyl ether and filtered.A recovered filtrate is separated from the solvent, refined with ethanoland recrystallized, to produce a white solid (16-OB) according to theformula of:

The product 16-OB is blended with carbazole, palladium acetate,phosphine, sodium tertiary butyrate and o-xylene, and subjected toreflux reaction in a nitrogen atmosphere. At the end of the reaction, areaction product is extracted in chloroform, washed with distilledwater, refined by a column chromatography using chloroform andn-hexanone at a ratio of 1:2, and then recrystallized in ethanol, toproduce a white solid (16-OKB) according to the formula of:

[Synthesis of a Carrier-Transporting Liquid Crystal TPD-8(N,N′-diphenyl-N,N′-(4-octyloxyphenyl)-1,1′-biphenyl-4,4′-diamine)]

At first, p-iodophenol is dissolved in cyclohexane, potassium carbonate,and 1-iodine octane are added to the cyclohexane, and then the liquid issubjected to reflux reaction in a nitrogen atmosphere. At the end of thereaction, a brown liquid is obtained by filtration. The brown liquid isrefined to a light yellow liquid by column chromatography using n-hexaneas an eluent. OIB (octyl iodobenzene) is produced by drying the refinedyellow liquid under vacuum.

OIB is mixed with N,N′-diphenyl benzine, palladium acetate,tri-tert-butylphosphine, sodium tertiary butyrate and o-xylene, and themixture is subjected to reflux reaction in a nitrogen atmosphere. At theend of the reaction, a reaction product is extracted in chloroform andwashed with water. The reaction product is refined to a colorlesstransparent viscous matter by column chromatography using chloroform andn-hexane at a ratio of 1:1. Thereafter, the product is freeze-dried andrecrystallized to a white solid (TPD-8) in 2-propanol.

[Synthesis of a Bipolar Carrier-Transporting Liquid Crystal 8-PNP-O12(2-4,2-(4′-octylphenyl)-6-dodecyloxy naphthalene)]

After 6-bromo-2-naphthol is dissolved in cyclohexanone, potassiumcarbonate and 1-bromo dodecane are added to the liquid, and subjected toreflux reaction in a nitrogen atmosphere. At the end of the reaction, areaction product is dissolved in diethanol, and filtered. A recoveredfiltrate is separated from the solvent, refined with methanol, and thenrecrystallized, to produce a white solid (12 NaB) according to theformula of:

4-bromo-n-octyl benzene is dissolved in tetrahydrofuran, cooled in anitrogen atmosphere to a sub-zero temperature, and reacted withn-butyllithium at 0° C. The reaction product is re-cooled at a sub-zerotemperature, and then reacted with2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxy borane at a roomtemperature. Distilled water is added to the reaction product at the endof the reaction, and then the reaction product is washed with chloroformand salty water, and refined by a column chromatography using chloroformand n-hexanone at a ratio of 1:2, to produce a colorless transparentliquid (8 BB) according to the formula of:

Both 12 NaB and 8 BB are dissolved in tetrahydrofuran, and reacted witha potassium carbonate aqueous solution and Pd(PPh₃)₄ at a warmtemperature. After distilled water is added to the reaction product atthe end of the reaction, the reaction product is washed with chloroformand salty water, and then refined by a column chromatography usingchloroform and n-hexanone at a ratio of 1:2, to produce a white solid(8-PNP-O12) according to the formula of:

Example 1

After an ITO film was laid on a glass substrate (a transparent substrate1), the substrate was washed. A positive resist material applied ontothe substrate by a spin coater and then annealed at 100° C. for 50minutes, to form a resist film. The resist film was irradiated 10seconds with a ultraviolet ray, using a photomask having a predeterminedpattern. The irradiated resist film was developed by washing withion-exchanged water to flush solubilized resist material. Thereafter,the glass substrate was chemically etched, and the remaining resist filmwas dissolved off the substrate, so as to shape the ITO film (atransparent electrode 2) to a striped pattern.

After the ITO layer is patterned, an organic luminous substance MEH-PPV[poly(2-methoxy-5-ethyl hexoxy)-1,4-phenylenevinylene] was deposited onthe substrate to thickness of 100 nm and then rubbed. A thin Al film wasvapor deposited as a patterned backside electrode 5 on another glasssubstrate, and then MEH-PPV was deposited to thickness of 100 nm andrubbed. These glass substrates were piled up and bonded together withepoxy resin except for a liquid crystal injecting hole. A cell gapbetween the substrates was adjusted to 900 nm.

A liquid crystal prepared by dispersing 12-OKB in 5 CB at a ratio of 10wt. % was used as an organic luminous substance. 12-OKB was a nematicliquid crystal, which was transferred to a liquid crystal phase near aroom temperature in a state incorporated in 5 CB. Schlieren texture wasobserved at ratios of 5 wt. %, 10 wt. % and 20 wt. %.

MEH-PPV as an electron-transporting luminescent compound was synthesizedthrough 2-2-1,1-(2′-ethyl-hexyloxy)-4-methoxybenzene (EHMB) and then2-2-2,1,4-bis(chloromethyl)-2-(2′-ethyl-hexyloxy)-5-methoxybenzene(BCMB) as follows:

At first, 3-bromomethyl heptane dissolved in ethanol was dropped in anethanol liquid dissolving methoxyphenol and potassium hydroxide thereinin a nitrogen gas stream. After 3-bromomethyl heptane was completelydropped, the liquid was refluxed 24 hours at 80° C. in an oiling bath.After the reaction, the liquid was filtered, the filtrate was recovered,and the solvent was removed in an evaporator. Chloroform was added to aremaining liquid. The liquid was washed with 1N dilute hydrochloric acidaqueous solution, 1N sodium hydroxide aqueous solution and then water.Thereafter, the washed matter was dried 8 hours at 70° C. under vacuum.The obtained product was light yellow, and identified as EHMB by ¹H-NMRand elemental analysis. A yield ratio was 82.3% in this case.

Thereafter, EHMB dissolved in 1,4-dioxane was dropped in a formaldehydesolution (37%) and hydrochloric acid (37%) kept at 0° C. After EHMB wascompletely dropped, the liquid was stirred 18 hours at a roomtemperature. A formaldehyde solution and hydrochloric acid were furtheradded to the liquid at a period 10 hours after initiation of thereaction, and then the liquid was refluxed 5 hours in an oiling bathafter 18 hours. When the reaction was finished, a reaction product wasextracted in chloroform and washed with 1N-sodium hydroxide aqueoussolution and then water, and the solvent was removed in an evaporator.After hot methanol was added to the processed liquid, the liquid wasleft as such at a room temperature and then put in a freezing chamber. Awhite coarse crystal was obtained. The coarse crystal was refined bydissolving it in methanol and then recrystallizing, washed with coldmethanol, and then dried 8 hours at 40° C. under vacuum. A product waswhite solid, and identified as BCMB by ¹H-NMR and elemental analysis. Anyield ratio was 28.6%.

After BCMB and tert-butyl benzyl chloride (as an endcap agent) wasdissolved in THF, potassium tert-butoxide was added to the liquid, andthe liquid was stirred 30 hours at a room temperature in a nitrogenatmosphere. When the reaction was finished, THF was quantitativelydecreased to about 1/10 in an evaporator, so as to precipitate redsediment by injection of methanol (a poor solvent). A red polymer wasproduced by drying a filtrate 8 hours at 40° C. under vacuum. Thepolymer was refined three times by reprecipitation purification usingchloroform (a good solvent) and methanol (a poor solvent). The obtainedpolymer was identified as MEH-PPV by IR spectrum and elemental analysis.A yield ratio was 31/9%, weight average molecular Mw was 1,190,000, anda Mw/Mn ratio (Mn: number average molecular weight) was 2.7.

A liquid crystal was prepared by dispersing 10 mass % of 12-OKB in4-cyano-4′-pentylbiphenyl (5 CB) 12-OKB in a state incorporated in 5 CBwas transferred to a liquid crystalline phase at a temperature near aroom temperature, and behaved as a nematic liquid crystal whoseSchlieren texture was observed in concentration of 5 mass %, 10 mass %and 20 mass %.

The bonded substrates (an empty cell) were dried 1 hour at a roomtemperature, received in Petri dish filled with the liquid crystal, andset in a desiccator. The empty cell was evacuated by a vacuum pump, andits liquid crystal injecting hole was dipped in the liquid crystalreserved in Petri dish, so that the liquid crystal slowly flowed fromPetri dish into the empty cell.

After a sufficient amount of the liquid crystal was poured in the emptycell, the liquid crystal injecting hole was hermetically sealed withadhesives 8 (epoxy resin), as shown in FIG. 3. Thereafter, the cell wasdried 1 hour.

Polarizing plates 9,10 were respectively laid on both surfaces of thecell 7, so that each polarizing plane was set parallel to the other. Inthis case, the surface of the cell was dark under power-off condition,but turned to light by application of 15V. Polarizing plates 9,10 werelaid on both surfaces of the cell 7, so that each polarizing planecrosses to the other with a right angle on the contrary. In this case,the surface of the cell was light under power-off condition, but turnedto dark by application of 15V. Turning to dark or light proved facultyas a liquid crystal display device. Light emission originated in MEH-PPVwas observed, when the cell was charged with a voltage of 35V or higher.Luminance of 0.175 cd/m² at most was gained at 131V with an externalquantum efficiency of 0.043%. Faculty of 12-OKB as a hole-transportingsubstance was recognized by such the light emission.

Example 2

A cell 7 was fabricated in the same way as Example 1 except for usingPEDOT doped with PSS (polystyrene sulfonate) instead of MEH-PPV at aside of the ITO substrate. PEDOT and PSS are respectively of:

Polarizing plates 9,10 were respectively laid on both surfaces of thecell 7, so that each polarizing plane was set parallel to the other. Inthis case, the surface of the cell was dark under power-off condition,but turned to light by application of 5V. Polarizing plates 9,10 werelaid on both surfaces of the cell 7, so that each polarizing planecrossed to the other with a right angle on the contrary. In this case,the surface of the cell was light under power-off condition, but turnedto dark by application of 5V. Turning to dark or light proved faculty asa liquid crystal display device. Light emission originated in MEH-PPVwas observed, when the cell was charged with a voltage of 15V or higher.Luminance of 1.04 cd/m² at most was gained at 90V with an externalquantum efficiency of 0.045%.

Example 3

An organic electroluminescent display device, which also act as atransmission liquid crystal display device, was fabricated by pouring aliquid crystal in an empty cell in the same way as Example 2 except forformation of s transparent backside electrode instead of an Al layerwithout formation of an Al layer.

Polarizing plates 9,10 were respectively laid on both surfaces of thecell 7, so that each polarizing plane was set parallel to the other. Inthis case, the surface of the cell was dark under power-off condition,but turned to light by application of 14V. Polarizing plates 9,10 werelaid on both surfaces of the cell 7, so that each polarizing planecrosses to the other with a right angle on the contrary. In this case,the surface of the cell was light under power-off condition, but turnedto dark by application of 14V. Turning to dark or light proved facultyas a liquid crystal display device. Light emission originated in MEH-PPVwas observed, when the cell was charged with a voltage of 40V or higher.Luminance of 0.7 cd/m² at most was gained at 155V with an externalquantum efficiency of 0.019%.

Example 4

A cell was fabricated in the same way as Example 2 except for using8-OCu instead of 12-OKB.

Polarizing plates 9,10 were respectively laid on both surfaces of thecell 7, so that each polarizing plane was set parallel to the other. Inthis case, the surface of the cell was dark under power-off condition,but turned to light by application of 13V. Polarizing plates 9,10 werelaid on both surfaces of the cell 7, so that each polarizing planecrossed to the other with a right angle on the contrary. In this case,the surface of the cell was light under power-off condition, but turnedto dark by application of 13V. Turning to dark or light proved facultyas a liquid crystal display device. Light emission originated in 8-OCuwas observed, when the cell was charged with a voltage of 60V or higher.Luminance of 0.5 cd/m² at most was gained at 140V.

Example 5

A cell was fabricated in the same way as Example 1 except for using PVK(polyvinylcarbazole) and cumarin-6 instead of 12-OKB. PVK and cumarin-6are respectively of:

Polarizing plates 9,10 were respectively laid on both surfaces of thecell 7, so that each polarizing plane was set parallel to the other. Inthis case, the surface of the cell was dark under power-off condition,but turned to light by application of 15V. Polarizing plates 9,10 werelaid on both surfaces of the cell 7, so that each polarizing planecrossed to the other with a right angle on the contrary. In this case,the surface of the cell was light under power-off condition, but turnedto dark by application of 15V. Turning to dark or light proved facultyas a liquid crystal display device. Light emission originated incumarin-6 was observed, when the cell was charged with a voltage of 70Vor higher. Luminance of 0.6 cd/m² at most was gained at 130V.

For comparison, a cell was fabricated without use of PVK. In this case,an initial voltage for light emission originated in cumarin-6 increasedto 110V.

Decrease of the initial voltage means that PVK mixed in the liquidcrystal act as a carrier-transporting substance, while cumarin-6 hasfaculty as a luminous substance.

Example 6

A cell was fabricated in the same way as Example 1 except for using TPD(tetraphenyl diamine) instead of 12-OKB. TPD is of:

Polarizing plates 9,10 were respectively laid on both surfaces of thecell 7, so that each polarizing plane was set parallel to the other. Inthis case, the surface of the cell was dark under power-off condition,but turned to light by application of 13V. Polarizing plates 9,10 werelaid on both surfaces of the cell 7, so that each polarizing planecrossed to the other with a right angle on the contrary. In this case,the surface of the cell was light under power-off condition, but turnedto dark by application of 13V. Turning to dark or light proved facultyas a reflecting liquid crystal display device. Light emission originatedin MEH-PPV was observed, when the cell was charged with a voltage of 50Vor higher. Luminance of 1.2 cd/m² at most was gained at 120V. The resultproved that the liquid crystal layer containing a low moleculecarrier-transporting substance dispersed therein has faculty as acarrier-transporting layer.

Example 7

Two glass substrates coated with ITO patterns were prepared by the sameway as Example 1. PEDOT doped with PSS (polyethylene sulfonate) wasdeposited as a thin layer of 100 nm in thickness on one glass substrateand then rubber, while MEH-PPV was deposited as an electroluminescentlayer of 100 nm in thickness and then rubbed. These glass substrateswere piled up with a cell gap of 1 μm in the manner such that the PEDOTlayer faced to the MEH-PPV layer, and bonded together with epoxy resinexcept for a liquid crystal injecting hole. In this example, a liquidprepared by dispersing TPD-8 in 5 CB at a ratio of 5 mass % was used asa carrier-transporting substance.

TPD-8 was gradually heated at a speed of 20° C./minute, held 5 minutesat a predetermined temperature and cooled at a speed of 3° C./minute ona hot stage for observation of its crystallinity. TPD-8 solely did notbehave as a liquid crystal. However, when TPD-8 disposed in 5 CB at aratio of 5 mass % was subjected to the same examination, phasetransition was detected at 35° C. on a cooling stage. The phasetransition temperature lowered as increase of concentration of TPD-8 in5CB. The result proves that TPD-8 was transformed to a liquid crystal ata room temperature in the state incorporated in 5CB. TPD-8 dispersed in5CB at a ratio of 5, 10 or 20 mass % was a nematic liquid crystal havingSchlieren texture. The phase transition may be derived from collapse ofstructure of 5CB due to steric hindrance caused by triphenylaminestructure of TPD-8 or by magnitude of a rotation angle of an octyloxyunit at a p-position.

The bonded substrates (an empty cell) were dried 1 hour at a roomtemperature, received in Petri dish filled with the liquid crystal, andset in a desiccator. The empty cell was evacuated by a vacuum pump, andits liquid crystal injecting hole was dipped in the liquid crystalreserved in Petri dish, so that the liquid crystal slowly flowed fromPetri dish into the empty cell. After a sufficient amount of the liquidcrystal was poured in the empty cell, the liquid crystal injecting holewas hermetically sealed with adhesives 8 (epoxy resin), as shown in FIG.4. Thereafter, the cell was dried 1 hour.

Polarizing plates 9,10 were respectively laid on both surfaces of thecell 7, so that each polarizing plane was set parallel to the other. Inthis case, the surface of the cell was dark under power-off condition,but turned to light by application of 18V. Polarizing plates 9,10 werelaid on both surfaces of the cell 7, so that each polarizing planecrosses to the other with a right angle on the contrary. In this case,the surface of the cell was light under power-off condition, but turnedto dark by application of 18V. Turning to dark or light proved facultyas a liquid crystal display device. Light emission originated in MEH-PPVwas observed, when the cell was charged with a voltage of 28V or higher.Luminance of 2.5 cd/m² at most was gained at 47V. Faculty of 12-OKB as ahole-transporting substance was recognized by such the light emission.

Example 8

PSS-doped PEDOT was used as an oriented film to liquid crystal insteadof MEH-PPV. An electroluminescent liquid crystal was prepared by adding10 mass % 12-OKB and 0.3 ml % Ir(ppy)₃ to 5CB instead of TPD-8 andheated at 50° C. An electroluminescent cell was fabricated in the sameway as Example 7.

Polarizing plates 9,10 were respectively laid on both surfaces of thecell 7, so that each polarizing plane was set parallel to the other. Inthis case, the surface of the cell was dark under power-off condition,but turned to light by application of 10V. Polarizing plates 9,10 werelaid on both surfaces of the cell 7, so that each polarizing planecrosses to the other with a right angle on the contrary. In this case,the surface of the cell was light under power-off condition, but turnedto dark by application of 10V. Turning to dark or light proved facultyas a liquid crystal display device. Light emission originated inIr(ppy)₃ was observed, when the cell was charged with a voltage of 57Vor higher. Luminance of 17.8 cd/m² at most was gained at 92V. Theresults prove that 5CB dispersing 12-OKB therein behaved as ahole-transporting substance, while Ir(ppy)₃ behaved as a light-emittingsubstance.

The produced organic electroluminescent device had voltage-currentcharacteristic as shown in FIG. 5 and relationship of emission intensitywith voltage as shown in FIG. 6.

The organic electroluminescent display device proposed by the presentinvention can be also driven as a liquid crystal display device, since acarrier-transporting layer and/or an organic luminous layer havingfaculty as a liquid crystal element is laminated on a transparentsubstrate. Due to the faculty as a liquid crystal element, the newdisplay device is used as a liquid crystal display device at a day timeor in a lighted place where an image is distinctly observed, and also asan electroluminescent display device in a dark place. Such switching ofdisplay mechanism saves power consumption. Furthermore, the newelectroluminescent display device can be fabricated in a thin statewithout complication of process, since a liquid crystal substance isincorporated in the carrier-transporting layer and/or the organicluminous layer of the organic electroluminescent element itself.

1. An organic electroluminescent display device comprising at least oneorganic luminous layer sandwiched between a transparent electrode and abackside electrode, wherein said display device is driven as a liquidcrystal display device at a voltage lower than a light emissioninitiating potential of the organic luminous layer and as anelectroluminescent display device at a voltage higher than a lightemission initiating potential of the organic luminous layer in responseto magnitude of an applied voltage, wherein the organic luminous layercomprises at least one electroluminescent liquid crystal comprising atleast one chemical compound represented by general formulas (I), (II),(III) or (V):

wherein R¹ is a straight chained alkyl group containing 1-20 carbonatoms, R² to R⁹ are each independently selected from hydrogen or analkyl group containing 1-3 carbon atoms, and Ar¹ is a substituted ornon-substituted aryl group containing 6-14 carbon atoms;

wherein R¹⁰ and R¹¹ are each independently selected from straightchained alkyl groups containing 1-20 carbon atoms, and Ar² and Ar³ areeach independently selected from substituted or non-substituted arylgroups containing 6-14 carbon atoms;

wherein R¹² is a straight chained alkyl group containing 1-20 carbonatoms, and R¹³, R¹⁴, R¹⁵, R¹⁶ and R¹⁷ are each independently selectedfrom hydrogen and alkyl groups containing 1-3 carbon atoms;

wherein R²⁰ is a straight chained alkyl group containing 1-20 carbonatoms, and Ar⁶, Ar⁷, Ar⁸, Ar⁹ and Ar¹⁰ are each independently selectedfrom substituted or non-substituted aryl groups containing 6-14 carbonatoms.
 2. The organic electroluminescent display device of claim 1,wherein the electroluminescent liquid crystal comprises the chemicalcompound represented by Formula-(I), and further wherein, R², R³, R⁴,R⁵, R⁶, R⁷, R⁸ and R⁹ are each hydrogen, Ar¹

and R¹ is —(CH₂)₇—CH₃.
 3. The organic electroluminescent display deviceof claim 1, wherein the electroluminescent liquid crystal comprises thechemical compound represented by Formula-(I), and further wherein, R²,R³, R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ are each hydrogen, Ar¹ is

and R¹ is —(CH₂)₁₁—CH₃.
 4. The organic electroluminescent display deviceof claim 1, wherein the electroluminescent liquid crystal comprises thechemical compound represented by Formula-(I), and further wherein, R²,R³, R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ are each hydrogen, Ar¹ is

and R¹ is —(CH₂)₁₅—CH₃.
 5. The organic electroluminescent display deviceof claim 1, wherein the electroluminescent liquid crystal comprises thechemical compound represented by Formula-(II), and further wherein, Ar²and Ar³ are each

R¹⁰ is —CH₃, and R¹¹ is —(CH₂)₁₇—CH₃.
 6. The organic electroluminescentdisplay device of claim 1, wherein the electroluminescent liquid crystalcomprises the chemical compound represented by Formula-(III), andfurther wherein, R¹² is —(CH₂)₇—CH₃, R¹³, R¹⁴, R¹⁵ and R¹⁷ are eachhydrogen, and R¹⁶ is —CH₃.
 7. The organic electroluminescent displaydevice of claim 1, wherein the electroluminescent liquid crystalcomprises the chemical compound represented by Formula-(V), and furtherwherein, Ar⁸ is

Ar⁶ and Ar⁹ are each,

Ar⁷ is

Ar¹⁰ is

and R²⁰ is —(CH₂)₇—CH₃.